I think the issue in these types of conversations is how the concept of racism/being racist is perceived.
It is commonly portrayed in white media and by white people as a conscious purposeful act, like murder, something done to someone, an individual act to hurt or be offended by or not. This is reductive, ignoring how institutional and ingrained it is within our society, ignoring how it tinges our reality and our perception of it. This article by resistracism fleshes out this idea better.
It's similar to sexism - as a woman it is easy to see the old boy's network that prevents access, the constant micro aggression against myself as a person, the disturbing representations in the media, the violence which is accepted in the media and by society, the concerns/thoughts/plans for my safety that men do not have to deal with, the treatment of my words as not as human as a man's. I've pointed it out to many men who completely miss it until it is pointed out - it's not a part of their mental framework.
It's the same here with racism (or xenophobia, or heterosexism, or cisexism, or ableism, pick an oppression dynamic), there is a historical network preventing accessing, safety concerns that others do not have to deal with, the treatment as less than human, issues with representation in media and elsewhere (repeated studies show that people believe fictional representations even more than non-fictional ones, in the latter people are more on their guard), and continuously grating micro aggression that wear people down, on top of the violence and what is normally seen as "racist" actions. I've had to point it out to white friends, and my white partner, who would never have noticed it, it isn't part of the framework and it's emphasised in an education system which boosts white (mostly male) achievements and whitewashes and ignores the achievements of other groups. It's dehumanizing from the big to the small, reinforcing the system. That is what "blacking up" is, it is reinforcing the system that allows this.
The news and governments and NGOs add to it. There was a sad article recently interviewing Congolese women discussing how they had to emphasis their rape statistics because that's what aid groups wanted to hear and what gave them access to aid, discussing a lack of representation and power - which leads to the dehumanisation that leads to rape - or social preventions doesn't get them anything. It's sad that they have to play the system/stereotype to get white agencies and governments to help because they are too blind in thinking they are good to see the racism that they are reinforcing and forcing others to reinforce for them.